1. Field of the Invention
The present invention relates to a method for recovering metals from waste catalysts, particularly to a method for recovering metals including nickel and aluminum from waste aluminum catalysts.
2. Description of the Related Art
In oil-refining industry, catalysts have been widely used in oil-cracking processes, with said catalysts generally have a carrier of alumina oxide (Al2O3), and with the carrier to immobilize metals in an active state, for example molybdenum or nickel, on surfaces thereof. Basically, those catalysts are aluminum catalysts.
Since said catalysts are easy to be ineffective due to the contamination and absorption of mass iron, phosphorus and vanadium during a catalysis process, a great amount of waste catalysts are generated during the processes of oil-refining, and which may lead to serious pollutions or ecological crisis while said waste catalysts are directly dumped without further processing. However, said waste catalysts are rich in valuable metals, such as vanadium, molybdenum, nickel, and aluminum, which are capable of being recovered and further in used in industries.
Conventional methods for processing waste catalysts include sodium-roasting process, roasting and acid leaching extraction, and alkali leaching extraction, wherein the sodium-roasting process is the most widely used among those methods.
However, nickel and aluminum in the waste catalysts are not easy to separate from the waste catalysts in the sodium-roasting process, since they are covered in sharp spar like dregs while the waste catalysts are sodium-roasted. Thus, the separation of nickel and aluminum from the sharp spar like dregs only can be achieved via processes of alkali leaching at a high pressure, acid leaching at a high pressure, or heating with arc furnace, which are complicated in process and wasteful in cost due to a great consuming of acid solution, alkali solution and energy (for example arc furnace). Accordingly, most industries have no choice but dump those sharp spar like dregs directly, however resulting in waste of resources and environment pollutions.
U.S. Pat. No. 4,495,157 entitled as “RECOVERY OF METAL VALUES FROM SPENT HYDRODESULFURIZATION CATALYSTS” discloses a conventional method using alkali leaching process to extract metals from waste catalysts. However, said alkali leaching process is poor in extraction rate due to a high amount of aluminum in the waste catalysts. Also said alkali leaching process is dangerous and costly since it has to be processed under a high pressure. Therefore, said alkali leaching process has plenty of disadvantages so as to be less useful to industry. Further, Chinese publication Patent No. 101631598 entitled as “METHOD OF RECOVERING VALUABLE METALS FROM THE VRDS SPENT CATALYST” discloses a conventional method of processing waste catalysts through processes, such as deoiling-roasting and oxidized-roasting, with metals being extracted from the waste catalysts respectively by further adjusting a pH value via acid leaching. However, said process of deoiling-roasting is wasteful in energy and cost with lots of acid solution being required as an adjustment of pH value. Moreover, said conventional method is poor in extraction rate of nickel and aluminum.
Hence, there is a pressing need for developing a new strategy, which can improve said disadvantages and effectively recover metal values, such as nickel and aluminum from waste aluminum catalysts.